LeakyBoot,
Yes... I put a D5 set of tracks on my D6-9u. I put sprockets on to match.
No need to change sprockets if you don't want to, suitable chains will still be available.
39 section chain is part #2S7577
40 section chain is part #2S7579
Both are 6.75" pitch with 5/8 pad bolting and both are considered non-current production.
Most get converted to D5 chain which is 6.91" pitch and need sprocket rim change to match.
Here ya go.
https://toledo.craigslist.org/hvo/d/caterpillar-d6/6501599771.html
39 VS 40 link ,my parts book only shows 39 link chain. Is the 40 for newer machine or different size idler? Looked at 9U the other day has 40 link , chain looks good the pins &bushings look good but idler set way ahead too far ahead, maybe wrong chain.
40 link would be correct 6.75" pitch chain with large front idler.
Ones less link if using 6.91" pitch chain.
Did just get a quote on new and is 1800 per chain. Thanks for replies. LB